Add a REINDEX NOCASE v2.15.1 migration and update v2.15.0 migration

[mikiher]

This is a migration aimed at fixing potential hidden old database index corruptiuons due to the faulty introduction of the unicode extension in v2.12.0. It perform a reindexing of all NOCASE indices in the database.

Migration v.2.15.0 is also updated to include the same fix, since we've seen that migration fail due these corruptions.

[advplyr]

Since we've identified a few indexes that should be added I wonder if we should try to put them in a migration or just put them in to sequelize like #3528

From my experience I have seen that sequelize will create the index if it doesn't exist but I'm not sure how full-proof that is. What do you think?

I'm leaning towards putting it in a migration to be safe but might be unnecessary.

[mikiher]

I would prefer a migration.

It's true that additional indices usually do not change the functionality of the database, just its performance characteristics, but it is still considered a good practice to have a migration - this keeps the database schema consistent with code versions, which is part of the point of using migrations.

For example, you know that when server version 2.17.0 is running, function X should be fast because it uses an index added in version 2.16.0 migration, but when the server version is 2.15.0, you expect X to be slow, because either the index was not yet added then, or because it was reverted due to a downward migration.

[advplyr]

My thoughts as well.
Tested this migration and looks good. Thanks!